Inverter- and-switched-capacitor-based squelch detector apparatus and method

ABSTRACT

A squelch detector includes is configured to receive a time-varying differential communication signal, and includes switched capacitors and an inverter configured to provide an indication of whether a level of the received communication signal is above or below a threshold value.

RELATED APPLICATIONS

The present application claims priority to U.S. application Ser. No.13/997,075, filed Jun. 21, 2013, entitled“INVERTER-AND-SWITCHED-CAPACITOR-BASED SQUELCH DETECTOR APPARATUS ANDMETHOD,” which claims priority to PCT Application No. PCT/MY2012/000073,entitled “INVERTER-AND-SWITCHED-CAPACITOR-BASED SQUELCH DETECTORAPPARATUS AND METHOD” the entire contents and disclosure of which arehereby incorporated by reference in their entirety.

TECHNICAL FIELD

This disclosure relates generally to electronic circuits. Moreparticularly but not exclusively, the present disclosure relates to asquelch detector circuit.

BACKGROUND

A squelch detector is typically used in a communication system having ahigh-speed serial interface, such as a Universal Serial Bus (USB) 2.0system. In such implementations, a squelch detector operates to detectthe presence of a differential communication signal on a serialinterface communication channel. To conserve power, the unusedcomponent(s) in the serial interface channel is usually turned OFF orotherwise powered down if the squelch detector detects that there is nocommunication signal being sent or received. If the power level of thecommunication signal drops below a given threshold level, the squelchdetector generates a detector output signal indicating that the channelis inactive, and the detector output signal is then used to power downthe unused component(s). If the power level of the communication signalis greater than the given threshold level, the squelch detector changesthe detector output signal to indicate an active status so as to powerup the component(s) in the communication system.

In USB 2.0 systems, the squelch detector is typically implemented with amixer stage and an amplifier stage. The mixer stage includes adifferential offset biasing input pair of transistors and a differentialinput pair of transistors. The differential offset biasing input pair oftransistors is coupled to two reference voltage levels (Vref and Vrefb),wherein the difference of the two reference voltage levels is thethreshold voltage (Vth) used to determine whether the communicationsignal on the communication channel is active or inactive. Thedifferential offset biasing input pair of transistors is coupled to thedifferential input pair of transistors to generate an output signal thatis the subtraction of the differential threshold voltage(Vth=Vref−Vrefb) from the differential communication signal (Vin−Vinb).The mixer stage's output signal (Vin−Vinb)−Vth is sent to the amplifierstage so as to provide/amplify the detector output signal that indicateswhether the differential communication signal is larger than thethreshold voltage Vth. If the peak-to-peak potential of the differentialcommunication signal is greater than the squelch detection thresholdvalue (e.g., the threshold voltage Vth), the detector output signal willbe high, thereby indicating that the communication signal is present onthe communication channel. Vice versa, if the peak-to-peak potential ofthe differential communication signal is less than the threshold voltageVth, the detector output signal of the squelch detector will be low,thereby indicating that the communication channel is inactive.

There are a number of drawbacks with the squelch detector describedabove. For example, random process variations on a chip can produce amismatch of the differential pairs of transistors, and the mismatch inturn may cause an undesirable input offset voltage. The undesirableinput offset voltage, which either adds to or subtracts from the tworeference voltage levels Vref and Vrefb, leads to an inaccurate or aninadequate tripping voltage range for the squelch detector.

Moreover, the implementation of differential input pairs of transistorsand the amplifier stage consumes a large amount of power due to staticpower used in current sources for biasing. An offset cancellationcircuit may be implemented to counteract the undesired input offsetvoltage, but the offset cancellation circuit itself also consumes power.

Also, in certain serial interface protocols, like USB 2.0, a large inputcommon mode range imposes a significant design challenge to keep all ofthe transistors in the squelch detector in saturation mode. From processto process, due to the change in transistor characteristics, a greatamount of effort has to be spent in tuning the squelch detector andother circuitry to ensure the transistors are operating in thesaturation region.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting and non-exhaustive embodiments are described with referenceto the following figures, wherein like reference numerals refer to likeparts throughout the various views unless otherwise specified.

FIG. 1 illustrates example signals that may be used in accordance withone embodiment of a squelch detector.

FIG. 2 is a diagram of a squelch detector that can operate with theexample signals of FIG. 1, in accordance with one embodiment.

FIG. 3 shows an example clock signal that can be used for the squelchdetector of FIG. 2, in accordance with one embodiment.

FIG. 4 is a diagram of a clock circuit that can be used to provide oneor more clock signals for the squelch detector of FIG. 2, in accordancewith one embodiment.

FIG. 5 is a diagram of another embodiment of a squelch detector.

FIG. 6 show example clock signals for the clock circuit of FIG. 4, inaccordance with one embodiment.

FIG. 7 is a block diagram that illustrates an example computer systemsuitable to practice the disclosed squelch detector, in accordance withvarious embodiments.

DETAILED DESCRIPTION

Embodiments of a squelch detector circuit and method are describedherein. In the following description, numerous specific details aregiven to provide a thorough understanding of embodiments. Theembodiments can be practiced without one or more of the specificdetails, or with other methods, components, materials, etc. In otherinstances, well-known structures, materials, or operations are not shownor described in detail to avoid obscuring aspects of the embodiments.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment. Thus, the appearances of the phrases “in oneembodiment” or “in an embodiment” in various places throughout thisspecification are not necessarily all referring to the same embodiment.Furthermore, the particular features, structures, or characteristics maybe combined in any suitable manner in one or more embodiments.

One embodiment provides a squelch detector that includes an inverter,capacitors, and switches. The embodiment of the squelch detector mayhave a switched capacitor sampling circuit topology that is able tosample rapidly varying differential signals and compare the differentialamplitude against a threshold value, which is a different capabilitythan that of conventional inverter and switched capacitor-based circuitsthat can only compare between two different static (or relativelyslow-varying) values. As such, the squelch detector of one embodimentmay detect whether differential amplitude of the communication signal islarger than a squelch threshold voltage level.

According to one embodiment, an apparatus comprises: a detector circuitto receive a time-varying differential communication signal, andincluding switched capacitors and an inverter to provide an indicationof whether a level of the received communication signal is above orbelow a threshold value.

According to one embodiment of the apparatus, the time-varyingdifferential communication signal includes a first signal and a secondsignal, and a peak-to-peak amplitude difference between the first andsecond signals provides the level of the communication signal that iscompared with the threshold value.

According to one embodiment of the apparatus, the capacitors include afirst capacitor coupled to receive the communication signal and a secondcapacitor coupled to the inverter, wherein the detector circuit furtherincludes: a first set of switches, responsive to a first phase of aclock, to close to enable the first capacitor to store a voltagecorresponding to the level of the communication signal and to enable thesecond capacitor to store a voltage corresponding to a differencebetween the threshold value and a trip level of the inverter; and asecond set of switches, responsive to a second phase of the clock andthat is an inverse to the first phase, to close to couple the firstcapacitor to the second capacitor to enable a difference between thestored voltages to be provided to the inverter, wherein the first set ofswitches is closed while the second set of switches is open and viceversa.

According to one embodiment of the apparatus, the inverter is coupled toprovide an output signal having a first state if the level of thecommunication signal is greater than the threshold value to indicateactivity on a communication channel that carries the communicationsignal, and wherein the inverter is coupled to provide the output signalhaving a second state, opposite to the first state, if the level of thecommunication signal is less than the threshold value to indicateinsufficient activity on the communication channel.

According to one embodiment of the apparatus, the first capacitor has alarger capacitance than a capacitance of the second capacitor.

According to one embodiment of the apparatus, the capacitance of thefirst capacitor is five times or more greater than the capacitance ofthe second capacitor.

According to one embodiment of the apparatus, the first set of switchesincludes: a first switch coupled between a first terminal of the firstcapacitor and a first pad that receives the first signal; a secondswitch coupled between a second terminal of the first capacitor and asecond pad that receives the second signal; a third switch coupledbetween a first terminal of the second capacitor and a third pad thatreceives a voltage having the threshold value; and a fourth switchcoupled between an output terminal of the inverter and a second terminalof the second capacitor at an input terminal of the inverter.

According to one embodiment of the apparatus, the second set of switchesincludes: a fifth switch coupled between ground and the first terminalof the first capacitor; and a sixth switch coupled between the secondterminal of the first capacitor and the first terminal of the secondcapacitor.

According to one embodiment, the apparatus further comprises at leastanother inverter, coupled to the inverter, to provide an invertedversion of an output of the detector circuit and to increase a gain ofthe detector circuit.

According to one embodiment, the apparatus further comprises a latchcircuit coupled to the inverter.

According to one embodiment, the apparatus further comprises a clockcircuit, coupled to the detector circuit, to receive input quadraturesignals and to generate the clock signal to have a frequency that is atleast double a frequency of each of the quadrature signals.

According to one embodiment, a method comprises: receiving, by adetector, a time-varying differential communication signal; operating afirst set of switches, in response to a first phase of a clock signal,to store in a first capacitor a first voltage level corresponding to thecommunication signal and to store in a second capacitor a second voltagelevel corresponding to a threshold level; operating a second set ofswitches, in response to a second phase of the clock signal, to provideto an inverter a third voltage level corresponding to a differencebetween the stored first and voltage levels; and generating, by theinverter in response to the provided third voltage level, an outputsignal to indicate whether an amplitude level the communication signalexceeds the threshold level.

According to one embodiment of the method, the generating the outputsignal by the inverter in response to the provided third voltage levelincludes: determining whether the provided third voltage level isgreater than a trip level of the inverter; if the third voltage level isdetermined to be greater than the trip level, generating the outputsignal to have a first state to indicate that the amplitude level of thecommunication signal exceeds the threshold level; and if the thirdvoltage level is determined to be less than the trip level, generatingthe output signal to have a second state, opposite from the first state,to indicate that the amplitude level of the communication signal isbelow the threshold level.

According to one embodiment, the method further comprises powering downa component of a computer system in response to the output signal havingthe second state.

According to one embodiment, the method further comprises: receivinginput quadrature signals each having an operating frequency; andgenerating, from the received quadrature signals, the clock signal tohave a clock frequency of at least twice the operating frequency.

According to one embodiment of the method, the time-varying differentialcommunication signal includes a first signal and a second signal; theoperating the first set of switches to store the first voltage levelcorresponding to the communication signal includes operating the firstset of switches to store in the first capacitor a peak-to-peak amplitudedifference between the first and second signals; and the operating thefirst set of switches to store the second voltage level corresponding tothe threshold level includes operating the first set of switches tostore in the second capacitor a voltage corresponding to a differencebetween the threshold level and a trip level of the inverter.

According to one embodiment of the method, the first and second phasesof the clock signal have opposite polarities to enable the first set ofswitches to be closed while the second set of switches are open and viceversa.

According to one embodiment, a system includes: a communicationinterface to support a communication channel that carries a time-varyingdifferential communication signal; aninverter-and-switched-capacitor-based detector circuit, coupled to thecommunication interface, to detect activity by the communication signalin the communication channel and to generate an output signal toindicate whether the activity is detected; and a component, coupled tothe detector, to receive the generated output signal and to power downat least a portion of the communication interface if the output signalindicates insufficient activity by the communication signal in thecommunication channel.

According to one embodiment of the system, the component includes aprocessor.

According to one embodiment of the system, the detector circuitincludes: an inverter to provide the output signal and having a triplevel; a first capacitor coupled to receive the communication signal anda second capacitor coupled to the inverter; a first set of switches,responsive to a first phase of a clock, to close to enable the firstcapacitor to store a voltage corresponding to a level of thecommunication signal and to enable the second capacitor to store avoltage corresponding to a difference between a threshold value and thetrip level of the inverter; and a second set of switches, responsive toa second phase of the clock and that is an inverse to the first phase,to close to couple the first capacitor to the second capacitor to enablea difference between the stored voltages to be provided to the inverter,wherein the output signal indicates that there is activity thecommunication signal in the communication channel if the differencebetween the stored voltages provided to the inverter is above the triplevel of the inverter.

According to one embodiment, the system further comprises a clockcircuit, coupled to the detector circuit, to receive input quadraturesignals and to generate the clock signal to have a frequency that is atleast double a frequency of each of the quadrature signals.

Referring first to FIG. 1, voltage signals Vin and Vinb togethercomprise a time-varying differential communication signal that can besent/received over a communication channel. The differentialcommunication signal (Vin−Vinb) can be used, for example, in acommunication channel of a communication system having a high-speedserial interface, such as a Universal Serial Bus (USB) 2.0 system orother communication system that operates using differential signaling.

The differential communication signal has a peak-to-peak (pp) amplitudeVdiff=Vin−Vinb. The difference between two reference voltage levels Vrefand Vrefb is the squelch threshold voltage level Vth that is used todetermine whether the communication signal on the communication channelis active or inactive. For example, the communication channel may bedeemed to be active if Vdiff>Vth and may be deemed to be inactive ifVdiff<Vth.

Referring now to FIG. 2, shown generally at 200 is a squelch detector ofone embodiment. In one embodiment, the squelch detector 200 includes twocapacitors (C1 and C2), six switches (S1-S6), and an inverter 202.

The switch S1 is coupled between ground and a node N4. The switch S2 iscoupled between a first pad (or other terminal) 204 that receives thesignal Vinb and the node N4. The first capacitor C1 has a first terminalcoupled to the node N4 and a second terminal coupled to a node N3. Theswitch S3 is coupled between a second pad (or other terminal) 206 thatreceives the signal Vin and the node N3. The switch S4 is coupledbetween the node N3 and a node N2. The switch S5 is coupled between athird pad (or other terminal) 208 that has/receives the thresholdvoltage Vth and a node N2.

The second capacitor C2 has a first terminal coupled to the node N2 andsecond terminal coupled to a node N1. In one embodiment, the capacitor Cis approximately five times larger or more in capacitance than thecapacitor C2.

The switch S6 is coupled between the node N1 and an output terminal 210of the inverter 202. The node N1 is coupled to an input terminal of theinverter 202, and so with this configuration, the input of the inverter202 is short-circuited to its output if the switch S6 is closed. In oneembodiment, the output terminal 210 of the inverter 202 forms the outputterminal of the squelch detector 200, and therefore provides the outputsignal of the squelch detector 200.

In one embodiment, any one or more of the switches S1-S6 can includecomplementary metal oxide semiconductor (CMOS) transistors, such asP-type or N-type CMOS transistors having gate terminals that eachreceive and respond to phases of a clock signal that is used to controlthe turning ON or OFF of the CMOS transistors. Therefore, the switch isclosed (short circuit or connected) if the CMOS transistor is turned ON,and the switch is open (open circuit or disconnected) if the CMOStransistor is turned OFF.

In one embodiment, the gate terminals of the CMOS transistors arecoupled to receive either a clock pulse or an inverted clock pulse of aclock signal 300 shown in FIG. 3. The switches S2, S3, S5, and S6(forming a first set of switches) in FIG. 2 that are labeled with φ₁will be closed (connected) if the clock pulse is high (denoted as aclock phase φ₁ in FIG. 3), whereas the switches S1 and S4 (forming asecond set of switches) in FIG. 2 that are labeled with φ₂ will beclosed (connected) if the clock pulse is low (denoted as a clock phaseφ₂ in FIG. 3) Hence with this arrangement, the switches S2, S3, S5, andS6 may be CMOS transistors transmission gates (comprising of N-typeand/or P-type transistors) for which the gates are controlled by a clockpulse of a first polarity, and the switches S1 and S4 may be CMOStransmission gates that are controlled by a clock pulse of asecond/reverse polarity.

In operation, during the clock phase φ₁ in which the switches S2 and S3are closed and switches S1 and S4 are open, the capacitor C1 is coupledto the pad 206 having the voltage Vin and to the pad 204 having thevoltage Vinb, so as to sample the voltage difference (Vin−Vinb) betweenthe signals Vin and Vinb. This voltage difference (Vin−Vinb),corresponding to the peak-to-peak amplitude level of the communicationsignal, is a first voltage level that is stored in the capacitor C1.

Also in operation during the clock phase φ₁, in which the switches S5and S6 are closed and the switch S4 is open, a first terminal of thecapacitor C2 is coupled to the pad 208 having the voltage Vth (thesquelch threshold voltage level) and a second terminal of the capacitorC2 is coupled to the input terminal of the inverter 202, thereby causinga sampling of a voltage Vtrip (the trip point/level of the inverter 202)if the input of the inverter 202 is shorted to its output. Thecorresponding voltage difference Vth−Vtrip is a second voltage levelthat is stored in the capacitor C2. In one embodiment, the thresholdvoltage Vth may be directly set instead of doing the subtraction of Vrefand Vrefb.

During the clock phase φ₂ in which the switches S1 and S4 are closed andthe other switches are open, a first terminal of the capacitor C1 iscoupled to ground, and a second terminal will have the voltage potentialof Vin−Vinb. Since the capacitor C1 of one embodiment is selected to beat least five times larger than the capacitor C2, the capacitor C1appears or otherwise acts like a constant voltage source to capacitorC2. Because the capacitor C1 is coupled to the capacitor C2 during theclock phase φ₂, the point of connection between these two capacitorswill be forced to the potential of Vin−Vinb.

Since the capacitor C2 stores the voltage difference Vth−Vtrip, theinput terminal of the inverter 202 will receive or be otherwise providedwith a potential level of that is a difference between the voltagesstored in the capacitors C1 and C2. That is, the input terminal of theinverter 202 will see/receive a third voltage level(Vin−Vinb)−(Vth−Vtrip)=Vtrip+[(Vin−Vinb)−Vth]. If Vin−Vinb>Vth as aresult of activity on the communication channel that carries thecommunication signal, then the potential level at the input terminal ofthe inverter 202 is determined to be greater than Vtrip, and so theinverter 202 will output low (e.g., a first state of the output signalof the squelch detector 200) at the output terminal 210. If Vin−Vinb<Vthas a result of absent/insufficient activity by the communication signalon the communication channel, then the potential level at the inputterminal of the inverter 202 is determined to be lower than Vtrip, andthe inverter 202 will output high (e.g., a second state, opposite orinverse to the first state, of the output signal of the squelch detector200) at the output terminal 210.

The output signal of the inverter 202 is a negative of its input signal.If the output of a squelch detector is desired to be positive, then atleast one inverter can be coupled to the inverter 202, such as in acascaded manner, so as to provide an inverted version of the outputsignal of the inverter 202. FIG. 5 shows an embodiment of a squelchdetector 500 having a cascade of inverters 502 coupled to the outputterminal 210 of the inverter 202. Cascading inverters such as shown inthe embodiment of FIG. 5 can also increase the overall gain of thesquelch detector 500.

In one embodiment, a latch circuit 504 can be coupled to the cascade ofinverters 502. The latch circuit 504 can be used for example to store astate (e.g., high or low) of the output of the cascade of inverters 502,until the output changes state. An output of terminal 506 of the latchcircuit 504 provides the output signal (labeled as “squelch output”) ofthe squelch detector 500.

As explained above, the various embodiments of the squelch detectoroperate as a switched-capacitor sampling circuit that uses the clocksignal 300 to switch between the circuit connections during differentclock phases. According to the Nyquist sampling theorem, thesampling/clock frequency provided by the clock signal 300 of oneembodiment should be at least twice the highest frequency contained inthe differential communication signal.

For example, a USB 2.0 system may operate with an approximately 480 MHzclock, and so the sampling frequency should be approximately 960 MHz orgreater. In one embodiment, no additional/dedicated higher-frequencyclock is needed from a phase locked loop (PLL), since sending thehigher-frequency clock from the PLL to the squelch detector may consumeadditional power. Instead, one embodiment of the squelch detector mayuse existing clocking to provide the clock signal 300 with asufficiently high frequency.

For example, in one embodiment for a high-speed serial interface, thequadrature clocks clk0 and clk90 (at 0° and 90° phases, respectively) atthe operating frequency of 480 MHz are available. In a clock circuit 400of FIG. 4, these quadrature clocks clk0 and clk90 are utilized togenerate the sampling clock signal 300 with double the operatingfrequency. With USB 2.0 for instance, the 480 MHz clocks clk0 and clk90(respectively at 0° and 90°) can be logically operated on (e.g.,exclusively OR'ed together) to provide an output clock with frequency of960 MHz.

The clock circuit 400 includes an exclusive OR (XOR) gate 402 having twoinput terminals that respectively receive the quadrature input clocksignals clk0 and clk90. An output terminal of the exclusive OR gate 402provides a clock signal 600 that has double the frequency of the inputclock signals clk0 and clk90, such as shown by way of example in FIG. 6.The output terminal of the exclusive OR gate 402 is coupled to an inputterminal of an inverter 404, which in turn has an output terminalcoupled to a first input terminal of a non-overlapped clock generator406. The output terminal of the exclusive OR gate 402 is also coupled toa second input terminal of the clock generator 406. The clock generator406 of one embodiment is configured to receive clock and inverted clocksignals to generate non-overlapping clock signals as output signals. Forexample, the clock generator 406 outputs two clock signals “clock” and“clockb”, both of which have double the operating frequency of clocksignals clk0 and clk90. Either of the clock signals “clock” and “clockb”in FIG. 4 can be used as the clock signal 300 of FIG. 3.

The following example scenarios A, B, and C are provided so as tofurther illustrate operation of the various embodiments of the squelchdetector disclosed herein:

A. Vin is greater than Vinb by 0.15V (e.g., a value greater thanVth=0.1V), and with the sampling clock frequency=1 GHz, Vin=0.35V,Vinb=0.2V, and Vth=0. V.

-   -   During the clock phase φ₁ (the clock signal 300 is high), the        node N4 is coupled to Vinb=0.2V; the node N3 is coupled to        Vin=0.35V; the node N2 is coupled to Vth=0.1V; the node N1 has        the potential of Vtrip of the inverter 202 since the input        terminal of the inverter 202 is shorted to the output terminal        210. After sampling those voltages, during the clock phase φ₂        (the clock signal 300 is low), the node N4 is coupled to ground.        Since the capacitor C1 has the voltage difference of        Vin−Vinb=0.15V across it, the voltage at the node N3 becomes        0.15V. Due to the capacitor C1 having a larger capacitance than        the capacitor C2, the node N2 is forced to the voltage of 0.15V        as well.    -   The voltage at the node N1 changes from Vtrip to        Vtrip+[(Vin−Vinb)−Vth]=Vtrip+0.05V=0.5V+0.05V=0.55V. Since the        node N1 is 0.05V above the Vtrip of the inverter 202, the output        generated by the inverter 202 (at the output terminal 210) will        be low during the clock phase φ₂. The low output of the inverter        202 confirms or otherwise indicates that there is activity on        the communication channel (e.g., (Vin−Vinb)>Vth).

B. Vin is greater than Vinb by 0.05V (e.g., a value less than Vth=0.1V),and with the sampling clock frequency=1 GHz, Vin=0.25V, Vinb=0.2V, andVth=0.1V

-   -   During clock phase φ₁ (the clock signal 300 is high), the node        N4 is coupled to Vinb=0.2V; the node N3 is coupled to Vin=0.25;        the node N2 is coupled to Vth=0.1V; the node N1 has the        potential of Vtrip of the inverter 202 since the input terminal        of the inverter 202 is shorted to the output terminal 210. After        sampling those voltages, during the clock phase φ₂ (the clock        signal 300 is low), the node N4 is coupled to ground. Since the        capacitor C1 has the voltage difference of Vin−Vinb=0.05V across        it, the voltage at the node N3 becomes 0.05V. Due to the        capacitor C1 having a larger capacitance than the capacitor C2,        the node N2 is forced to the voltage of 0.05V as well.    -   The voltage at the node N1 changes from Vtrip to        Vtrip+[(Vin−Vinb)−Vth]=Vtrip−0.05V=0.5V−0.05V=0.45V. Since the        node N1 is 0.05V below the Vtrip of the inverter 202, the output        generated by the inverter 202 (at the output terminal 210) will        be high during the clock phase φ₂. The high output of the        inverter 202 confirms or otherwise indicates that activity is        absent or insufficient in the communication channel (e.g.,        (Vin−Vinb)<Vth).

C. Vin is less than Vinb, and with the sampling clock frequency=1 GHz,Vin=0.3V, Vinb=0.5V, Vth=0.1V.

-   -   During the clock phase φ₁ (the clock signal 300 is high), the        node N4 is coupled to Vinb=0.5V; the node N3 is coupled to        Vin=0.3; the node N2 is coupled to Vth=0.1V; the node N1 has the        potential of the Vtrip of the inverter 202 since the input        terminal of the inverter 202 is shorted to the output terminal        210. After sampling those voltages, during the clock phase φ₂        (the clock signal 300 is low), the node N4 is coupled to ground.        Since the capacitor C1 has the voltage difference of        Vin-Vinb=−0.2V across it, the voltage at the node N3 becomes        around −0.2V. Due to the capacitor C1 having a larger        capacitance than the capacitor C2, the node N2 is forced to the        voltage of −0.2V as well.    -   The voltage at the node N1 changes from Vtrip to        Vtrip+[(Vin−Vinb)−Vth]=Vtrip−0.3V=0.5V−0.3V=−0.2V. Since the        node N1 is 0.3V below the Vtrip of the inverter 202, the output        terminal 210 of the inverter 202 will be high. The high output        generated by the inverter 202 confirms or otherwise indicates        that activity is absent or insufficient in the communication        channel (e.g., (Vin−Vinb)<Vth).

The embodiments(s) of the squelch detector(s) disclosed herein provideat least the following features that are different from conventionalsquelch detectors:

-   -   Low power consumption, since various power-consuming components        of conventional squelch detectors are omitted;    -   No amplifier and current source are involved. Thus, there is no        static current, and instead dynamic current is consumed during        switching. Current consumption may be around 300 uA, for        example, as compared to conventional mixer and amplifier        stage-based architectures that consume 1-2 mA or higher due to        usage of current sources for biasing;    -   The circuit design of one embodiment of the squelch detector is        relatively simple compared to conventional mixer and amplifier        stage-based squelch detectors;    -   Conventional mixer and amplifier stage-based squelch detectors        attempt to match all of the devices in the circuit in order to        reduce the input offset voltage. On the contrary, there is no        stringent requirement on device matching of one embodiment of        the squelch detector disclosed herein, since the Vtrip of the        inverter 202 is already stored in the capacitor C2 during the        clock phase φ₁ and the operation is not dependent on the        matching of any device. The capacitor C1 is designed to be        relatively larger than the capacitor C2 so that the capacitor C1        appears to be a constant voltage source if the capacitor C1 is        coupled to the capacitor C2; and    -   There is simpler migration from process to process. This is        because the squelch detector of one embodiment does not require        the component devices to operate in the saturation region, as        compared to conventional mixer and amplifier stage-based squelch        detectors that are re-tuned when migrated to a new process, so        as to ensure all the devices are operating in the saturation        region.

Embodiments of the squelch detector(s) described herein may be used in anumber of implementations and applications. For example, mobile devices,including but not limited to smart phones, nettops, tablets and otherMobile Internet Devices (MIDs) may have circuit(s) that would benefitfrom improved squelch detection operation. In such implementations, thesquelch detector can be used to provide an output signal that triggersactivation or deactivation of various components based on whether thereis signal activity in a communication channel.

FIG. 7 is a block diagram that illustrates an example computer system700 suitable to practice the disclosed squelch detector circuit/methodof various embodiments.

As shown, the computer system 700 may include a power supply unit 702, anumber of processors or processor cores 704, a system memory 706 havingprocessor-readable and processor-executable instructions 708 storedtherein, a mass storage device 710 that may also store the instructions708, and a communication interface 712. For the purpose of thisapplication, including the claims, the terms “processor” and “processorcores” may be considered synonymous, unless the context clearly requiresotherwise.

In various embodiments of the present disclosure, at least one of theprocessors 704, including a controller, may generate or cause to begenerated a signal to trigger activation/deactivation of variouscomponents (such as powering down or powering up at least a portion ofthe communication interface 712 and/or other components) of the system700 in response to the processor 704 receiving or otherwise evaluatingthe state of the output signal provided by the squelch detector. Inother embodiments, various other components (internal or external to thesystem 700) may generate one or more of such signals in response to theoutput signal from the squelch detector.

The one or more mass storage devices 710 and/or the memory 706 maycomprise a tangible, non-transitory computer-readable storage device(such as a diskette, hard drive, compact disc read only memory (CDROM),hardware storage unit, flash memory, phase change memory (PCM),solid-state drive (SSD) memory, and so forth). The instructions 708stored in the mass storage devices 710 and/or the memory 706 may beexecutable by one or more of the processors 704.

The computer system 700 may also comprise input/output devices 714 (suchas a keyboard, display screen, cursor control, and so forth). In variousembodiments and purely by way of example, the I/O devices 714 mayinclude component(s) 718 that send/receive a differential communicationsignal or otherwise provide/support the communication channel on whichthe differential communication signal is carried, and the component(s)718 may themselves include or be otherwise coupled to the squelchdetector. The squelch detector and related circuitry (or othercomponents of the system 700) may alternatively or additionally belocated elsewhere in the computer system 700, and may comprise part orall of an integrated circuit. For instance, a detector 720 may comprisepart of a communication interface 712 and may include the embodiment(s)of the squelch detector described herein.

The various elements of FIG. 7 may be coupled to each other via a systembus 716, which represents one or more buses. In the case of multiplebuses, they may be bridged by one or more bus bridges (not shown). Datamay pass through the system bus 716 through the I/O devices 714, forexample, between the output terminal of the squelch detector and theprocessors 704. The output signal from the squelch detector may also besent between discrete chips on a Multi-Chip Package (MCP). In oneembodiment, such MCP could represent one or more processors 704 or anyother component of system 700. In one embodiment a portion or all of thememory 706 could be integrated on an MCP with one or more processors704. In one embodiment, one or more chips in system 700 may have asquelch detector.

The system memory 706 and the mass storage device 710 may be employed tostore a working copy and a permanent copy of the programminginstructions implementing one or more operating systems, firmwaremodules or drivers, applications, and so forth, herein collectivelydenoted as 708. The permanent copy of the programming instructions maybe placed into permanent storage in the factory, or in the field,through, for example, a distribution medium (not shown), such as acompact disc (CD), or through the communication interface 712 (from adistribution server (not shown)).

According to various embodiments, one or more of the depicted componentsof the system 700 and/or other element(s) may include a keyboard, LCDscreen, non-volatile memory port, multiple antennas, graphics processor,application processor, speakers, or other associated mobile deviceelements, including a camera.

The remaining constitution of the various elements of the computersystem 700 is known, and accordingly will not be further described indetail.

The above description of illustrated embodiments, including what isdescribed in the Abstract, is not intended to be exhaustive or to belimited to the precise forms disclosed. While specific embodiments andexamples are described herein for illustrative purposes, variousmodifications are possible. For example, the configuration andconnection of certain elements in various embodiments have beendescribed above in the context of high/low values of signals, responsesto rising/falling edges of signals, inverters to invert signals,specific types of logic gates and/or logic configurations, and so forth.In other embodiments, different configurations can be provided in viewof whether or not certain signals are inverted, whether certain changesin state are triggered in response to falling edges instead of risingedges or vice versa, different logic gate configurations, and so forth.

These and other modifications can be made in light of the above detaileddescription. The terms used in the following claims should not beconstrued to be limited to the specific embodiments disclosed in thespecification.

What is claimed is:
 1. An apparatus, comprising: means for receiving atime-varying differential communication signal; means for operating afirst set of switches, in response to a first phase of a clock signal,to store in a first capacitor a first voltage level corresponding to thecommunication signal and to store in a second capacitor a second voltagelevel corresponding to a threshold level; means for operating a secondset of switches, in response to a second phase of the clock signal, toprovide to an inverter a third voltage level corresponding to adifference between the stored first and second voltage levels; and meansfor generating, by the inverter in response to the provided thirdvoltage level, an output signal to indicate whether an amplitude levelof the communication signal exceeds the threshold level.
 2. Theapparatus of claim 1, wherein the means for generating the output signalby the inverter in response to the provided third voltage levelincludes: means for determining whether the provided third voltage levelis greater than a trip level of the inverter; means for, if the thirdvoltage level is determined to be greater than the trip level,generating the output signal to have a first state to indicate that theamplitude level of the communication signal exceeds the threshold level;and means for, if the third voltage level is determined to be less thanthe trip level, generating the output signal to have a second state,opposite from the first state, to indicate that the amplitude level ofthe communication signal is below the threshold level.
 3. The apparatusof claim 2, further comprising: means for powering down a component of acomputer system in response to the output signal having the secondstate.
 4. The apparatus of claim 1, further comprising: means forreceiving input quadrature signals each having an operating frequency;and means for generating, from the received quadrature signals, theclock signal to have a clock frequency of at least twice the operatingfrequency.
 5. The apparatus of claim 1, wherein the time-varyingdifferential communication signal includes a first signal and a secondsignal; wherein the means for operating the first set of switches tostore the first voltage level corresponding to the communication signalincludes means for operating the first set of switches to store in thefirst capacitor a peak-to-peak amplitude difference between the firstand second signals; and wherein the means for operating the first set ofswitches to store the second voltage level corresponding to thethreshold level includes means for operating the first set of switchesto store in the second capacitor a voltage corresponding to a differencebetween the threshold level and a trip level of the inverter.
 6. Theapparatus of claim 1, wherein the first and second phases of the clocksignal have opposite polarities to enable the first set of switches tobe closed while the second set of switches are open and vice versa.
 7. Adetector circuit comprising: an inverter; a first capacitor to, during afirst phase of a control signal, store a first voltage corresponding toa difference between first and second component signals of adifferential communication signal; and a second capacitor to, during thefirst phase of the control signal, store a second voltage correspondingto a difference between a threshold voltage and a trip voltage of theinverter; wherein the first and second capacitors are to, during asecond phase of the control signal after the first phase, provide athird voltage to an input terminal of the inverter that corresponds to adifference between the first voltage and the second voltage.
 8. Thedetector circuit of claim 7, wherein the second capacitor is coupledbetween the first capacitor and the input terminal of the inverter. 9.The detector circuit of claim 7, further comprising: a first inputterminal to receive the first component signal; a second input terminalto receive the second component signal; a threshold terminal to receivethe threshold voltage; a first switch coupled between the first inputterminal and a first terminal of the first capacitor; a second switchcoupled between the second input terminal and a second terminal of thefirst capacitor; and a third switch coupled between the thresholdterminal and a first terminal of the second capacitor, wherein a secondterminal of the second capacitor is coupled to the input terminal of theinverter; wherein the first, second, and third switches are to be closedduring the first phase of the control signal and are to be open duringthe second phase of the control signal.
 10. The detector circuit ofclaim 9, further comprising a fourth switch coupled between the inputterminal of the inverter and an output terminal of the inverter, whereinthe fourth switch is to be closed during the first phase of the controlsignal and is to be open during the second phase of the control signal.11. The detector circuit of claim 10, further comprising: a fifth switchcoupled between the first terminal of the first capacitor and a groundterminal; and a sixth switch coupled between the second terminal of thefirst capacitor and the first terminal of the second capacitor; whereinthe fifth and sixth switches are to be open during the first phase ofthe control signal and are to be closed during the second phase of thecontrol signal.
 12. The detector circuit of claim 7, wherein acapacitance of the first capacitor is greater than a capacitance of thesecond capacitor.
 13. The detector circuit of claim 12, wherein thecapacitance of the first capacitor is at least five times greater thanthe capacitance of the second capacitor.
 14. The detector circuit ofclaim 7, wherein the communication signal is a Universal Serial Bus(USB) communication signal.
 15. The detector circuit of claim 7, whereinthe inverter is to output a signal that indicates whether the differencebetween the first and second component signals is greater than thethreshold voltage based on the third voltage.
 16. A system comprising: acommunication interface to communicate a time-varying differentialcommunication signal including a first component signal and a secondcomponent signal; a squelch detector circuit coupled to thecommunication interface and including a detector element, the detectorcircuit to: during a first phase of a clock signal, sample a firstvoltage corresponding to a difference between the first and secondcomponent signals and sample a second voltage corresponding to adifference between a threshold voltage and a trip voltage of thedetector element; and during a second phase of the clock signal afterthe first phase, provide a third voltage to a detector element thatcorresponds to a difference between the first voltage and the secondvoltage, wherein the detector element is to determine whether thedifference between the first and second component signals is greaterthan the threshold voltage based on the third voltage.
 17. The system ofclaim 16, further comprising a component, coupled to the detector, toreceive an output signal from the detector element that indicateswhether the difference between the first and second component signals isgreater than the threshold voltage and to power down at least a portionof the communication interface if the output signal indicates that thedifference between the first and second component signals is less thanthe threshold voltage.
 18. The system of claim 16, wherein the squelchdetector circuit includes: a first switched capacitor to sample thefirst voltage during the first phase of the clock signal; a secondswitched capacitor to sample the second voltage during the first phaseof the clock signal; and a switch to couple the first capacitor inseries with the second capacitor and the detector element during thesecond phase of the clock signal.
 19. The system of claim 18, whereinthe detector element includes an inverter, wherein the switch is a firstswitch, and wherein the squelch detector circuit further includes: asecond switch to selectively couple an input terminal of the inverterwith an output terminal of the inverter during the first phase of theclock signal.
 20. The system of claim 18, wherein the switch is a firstswitch, and wherein the squelch detector further includes: a first inputterminal to receive the first component signal; a second input terminalto receive the second component signal; a threshold input terminal toreceive the threshold voltage; a second switch coupled between the firstinput terminal and a first terminal of the first switched capacitor toselectively pass the first component signal to the first terminal of thefirst switched capacitor during the first phase of the clock signal; athird switch coupled between the second input terminal and a secondterminal of the first switched capacitor to selectively pass the secondcomponent signal to the second terminal of the first switched capacitorduring the first phase of the clock signal; and a fourth switch coupledbetween the threshold input terminal and a first terminal of the secondswitched capacitor to selectively pass the threshold voltage to thefirst terminal of the second switched capacitor during the first phaseof the clock signal.
 21. The system of claim 20, wherein a secondterminal of the second switched capacitor is coupled to the inputterminal of the detector element during the first and second phases ofthe clock signal.
 22. The system of claim 20, wherein the squelchdetector circuit further includes a fifth switch coupled between thefirst terminal of the first switched capacitor and a ground terminal toselectively couple the first terminal of the first switched capacitor tothe ground terminal during the second phase of the clock signal.
 23. Thesystem of claim 18, wherein a capacitance of the first switchedcapacitor is at least five times greater than a capacitance of thesecond switched capacitor.
 24. The system of claim 16, furthercomprising a clock circuit, coupled to the squelch detector circuit, toreceive input quadrature signals and to generate the clock signal tohave a frequency that is at least double a frequency of each of thequadrature signals.
 25. The system of claim 16, further comprising anetwork interface and a display.